Make arithmetic operations n-ary when it makes sense

[gsimone]

eg:

// now
Mul(a, Mul(b, Mul(c, Mul(1, 3 )))
// then 
Mul(a, b, c, 1, 3 ) // becomes => a * b * c * 1. * 3.
Add(a, b, c, 1, 3 ) // becomes => a + b + c + 1. + 3.